Q.Meyer Lemon Tree Is Growing Thee Big Green Bulbs
Hello, I have Meyers lemon tree. It’s been producing for years. But the last couple years the lemons have been a lot smaller. Then I noticed that there were a few big green blubs growing. They looked rough on the outside (peel). Most never turned yellow. I am attaching one that did eventually turn yellow. Do you know if that is a bad sign?

Certified GKH Gardening Expert
If these are not fertilized, properly, a few times per year then under fertilization may be the issue. Improper balance of phosphorus, potassium, and sulfur will be to blame for most fruiting issues.
Here are some articles that will help:
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-not-fruiting.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-fruit-thick-rind.htm